1. Field of the Invention
This invention relates generally to a defibrillator system which is capable of defibrillation and patient monitoring. When used as a patient monitor, the defibrillator system includes a defibrillator, removable monitoring adapter, and monitoring electrodes. Monitoring electrodes communicate with the monitoring adapter and the defibrillator, providing means to observe the patient's electrocardiogram ("ECG"). A method of detecting the presence of the monitoring adapter by the defibrillator is also included. This invention also relates to the removable monitoring adapter. Defibrillators include manual defibrillators, semi-automatic defibrillators and automatic defibrillators. Semi-automatic defibrillators and automatic defibrillators are collectively referred to as "AEDs."
2. Description of the Prior Art
Sudden cardiac arrest ("SCA") is the leading cause of death in the United States. Most sudden cardiac arrest is caused by ventricular fibrillation ("VF"), in which the heart's muscle fibers contract without coordination, thereby interrupting normal blood flow to the body. The only known effective treatment for VF is electrical defibrillation, in which an electrical pulse is applied to the patient's heart. The electrical pulse must be delivered within a short time after onset of VF in order for the patient to have any reasonable chance of survival. Electrical defibrillation may also be used to treat pulseless ventricular tachycardia ("VT"). Accordingly, defibrillation is the appropriate therapy for any shockable rhythm, i.e., VF or pulseless VT.
One way of providing electrical defibrillation uses an external defibrillator. External defibrillators send electrical pulses to the patient's heart through electrodes applied to the patient's torso. External defibrillators are typically located and used in hospital emergency rooms, operating rooms, and in emergency medical vehicles. Of the wide variety of external defibrillators currently available, AEDs are becoming increasingly popular because they can be used by relatively inexperienced personnel. AEDs are also especially lightweight, compact and portable. AEDs are described, for example, in U.S. Pat. No. 5,607,454 to Cameron et al. entitled "Electrotherapy Method and Apparatus" and U.S. Pat. No. 5,591,213 to Morgan entitled "Defibrillator System Condition Indicator," the specifications of which are incorporated herein.
One example of a defibrillator that provides a mechanism for detecting monitoring electrodes is the Laerdal HeartStart 3000. The Heartstart 3000 measures impedance through the electrodes attached to the patient to determine whether the monitoring pads are attached. The HeartStart 3000 distinguishes between the patient and monitoring electrodes by establishing an impedance threshold for which patient impedances are on one side of the threshold and monitoring electrode impedances are on the other side of the threshold.
AEDs provide a number of advantages, including the availability of external defibrillation at locations where external defibrillation is not regularly expected, and is likely to be performed quite infrequently, such as in residences, public buildings, businesses, personal vehicles, public transportation vehicles, etc. However, many instances of symptomatic patients may occur where defibrillation is not required, or formally permitted, because the patient is not suffering SCA and does not meet the indications for use of an AED. Some AEDs could be used to monitor the patient's ECG using the defibrillation electrodes, but these electrodes are expensive and could represent some risk to a patient who doesn't need defibrillation. Yet, traditional low cost monitoring electrode are not appropriate, because most AEDs are not configured to detect or operate with monitoring electrodes.
What is needed is a simple, low cost and effective way of providing an ECG monitoring function in an AED, while ensuring that the AED does not attempt to send a defibrillation energy pulse through the monitoring electrodes.